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Fossils can reveal a lot about the past. For decades, scientists have studied fossils to uncover the events that might have occurred within history. Even though fossils are usually dried up and decomposed remnants of animal parts, Dale Greenwalt, a researcher from the National Museum of Natural History in Washington, D.C. discovered blood in the belly of a mosquito fossil. The mosquito lived 46 million years ago in a tropical forest.

The mosquito fossil was given to the museum as a gift. The female mosquito fossil, unlike many insect fossils, was preserved in a paper-thin piece of shale, which is a kind of rock that forms from the sediments located at the bottom of water. Insects tend to be better fossilized in dried tree sap known as amber. This mosquito fossil is believed to the only blood-engorged one to have been found within history.

"The chances that such an insect would be preserved in shale is almost infinitesimally small," Greenwalt explained according to FOX News.

In order to study the mosquito fossil, Greenwalt and his team used bismuth molecules, which is a heavy metal that is capable of vaporizing the chemicals in the fossils. The researchers then analyzed the vaporized chemicals with the help of a mass spectrometer, which identifies chemicals based on their atomic weights. From this technique, the researcher discovered porphyrins, which are organic compounds that exist in hemoglobin. The porphyrins were discovered in the fossil's belly, which indicated that the blood from the mosquito's last meal was preserved.

The researchers could not determine how the blood managed to preserve so well over the years. They theorized that the insect could have been trapped in water-suspended algae, which would then coat the mosquito right before it starts to fossilize. The study was published in the Proceedings of the National Academy of Science (PNAS).